The present invention is directed to a capacitive measuring assembly.
In many fields of technology, sports and medicine, it is necessary, in order to analyze specific phenomena to determine the forces that appear in a dynamic operation not only with regard to their total value, but also as to their distribution. Thus, for instance, it is extremely desirable for the manufacturer of automobile seats to know how the pressure distribution actually occurs on the surface and back rest of the seat when a person sits thereon in order that the seat can be made stronger or firmer in those places that bear a heavier load than in those places that bear a lighter load. In the manufacture of a ski, for example, it is desirable to know the force distribution in order to make it possible to adequately adapt the core construction to such distribution. Finally, in medicine, it is possible from the pattern of force distribution under the foot surfaces of a person being tested while walking to arrive at conclusions concerning orthopedic injuries or sensorial injuries as, for instance, in the case of diabetics, and to begin adequate therapeutical treatment.
For measuring the force distribution over surfaces, German Patent No. 25 29 475 discloses a matrix arrangement of lamellar capacitor elements disposed opposite to and intersecting each other with intercalation of an elastic dielectric. In this system, only vertical forces that is, only forces perpendicular to the capacitor surfaces, lead to measuring signals, since horizontal displacement of the lamellar capacitor elements effects no change of the surface dimensions opposite to each other. A disadvantage of such known system is the fact that the separate capacitor elements consisting of the surface sections directly opposite each other are mechanically interconnected so that local expansion is limited or measured patterns are adulterated.
It has been proposed in German Offenlegungsschrift No. 34 11 528 to uncouple the separate capacitor surfaces, to divide the lamellar capacitor surfaces into separate elements by notches, there being specially given in this publication, the suggestion of providing between the separate surfaces meandering current conductor paths through the corresponding notches. A very effective uncoupling of the separate surfaces is obtained by this arrangement in the sense that the pattern of force distribution to be measured is substantially more precise than formerly attained, but in this arrangement, forces parallel with the capacitor surface lead to a change of the effective capacitor surfaces, that is, to an adulteration of the vertical signal.
The above mentioned arrangements finally have in common that the three-dimensional measurement of force distribution that is desirable in many cases is not possible. For instance, it would be very interesting for the automobile tire industry, and of course also for all the other purposes described above, to know about the three-dimensional force distribution.
German Offenlegungsschrift No. 34 10 955 discloses a capacitive measuring system for determining forces wherein two groups of capacitor plates are disposed in a comblike arrangement and interlocked, being kept movable and parallel with each other. In the original state, when no forces act upon the capacitor plates or the fastening means thereof, the plates do not entirely overlap and thus, when relative forces are applied parallel with the surfaces of the plate sets, these become further interlocked whereby it is possible to measure an increase of capacity between the plates. In this arrangement, to avoid errors of measurement, the plates must be moved exclusively parallel with each other and thus, when using this known teaching, no three-dimensional force measurement is possible and it is not possible to eliminate forces in an inadmissible direction.